Appliances such as dishwashers and front-loading washing machines may have an access door with a gasket that must be compressed to seal water within a washing chamber. Small area, highly compliant gaskets may be sealed by pressure from the user during the closing of the door. The gasket may then be held in a compressed state by a latch mechanism.
Gaskets which require more force may be compressed by a latch mechanism having a lever operated by the user to engage a catch and draw the catch inward with a lever advantage to compress the gasket and hold the door shut.
A closing lever may be avoided in latch mechanisms that provide a bi-stable spring mechanism. During initial stages of closing of the door, closing force on the door is used to energize a spring. When the door closes past a balance point, the spring releases its energy in a manner to pull the door fully closed. An example of an over-center spring mechanism is described in U.S. Pat. No. 4,497,513 to Sasaki.
A variation on the bi-stable spring mechanism energizes the spring as the door is opened and holds that energy until the door is closed again. A balance point must still be crossed, and therefore a slight compression of the spring is required when the door is closed to release the energy. A latch of this kind is disclosed in U.S. Pat. No. 2,833,578 to Burke.
U.S. Pat. No. 6,290,270 to Spiessl shows a variation on Burke in which the latch spring is energized when the door is opened and held in the energized state by the rotation of a hook cam. When the door is closed, the hook cam is rotated by a catch element to release the energized spring by moving a rim of the hook cam past a stop. This design reduces the force required to close the door by eliminating the need to compress a bi-stable spring past the balance point during door closure. In this design, the hook cam must be held on a lever, and the energized spring moves the lever and hook cam.
U.S. Pat. No. 7,306,266 to Hapke, assigned to the same assignee as the present invention and hereby incorporated by reference, provides a latch that supports a rotating hook cam on a linear carriage rather than a lever, reducing the bending forces and permitting the carriage element to be manufactured of thermoplastic material.
In these latter two designs, the rotating hook cam is held in its energetic state, before receipt of the catch element and closure of the door, by a stop abutting an outer surface of the hook cam. When the hook cam rotates with engagement of the catch element, the hook cam rotates so that a reduced diameter portion of the hook cam aligns with the stop allowing movement of the hook cam in retraction to compress the door gasket.
The high forces between the hook cam and this stop can generate significant friction and accordingly it is known to use a rotating wheel for the stop to reduce sliding friction between the stop and hook cam. However reducing this friction increases the chance that the hook cam will accidentally shift in position independent of engagement of the catch element preventing proper operation in the future.